Internet advertising has become a significant source of revenue for publishers of electronic content. Publishers and advertisers alike value the precise information that internet advertising provides. For advertisers, it gives more information on the return they receive from the resources spent on the advertisements (ads). For publishers, the more users view and click on ads on the publishers' websites, the more the publishers can earn. Thus, the more directed the ads are to the user consuming the publisher content, the more effective the ads can be for both parties. Such techniques can also benefit the users by presenting them with ad content that is particularly useful to them, and aimed at addresses their current needs.
Publishers often have information about the users viewing their sites that can be used to direct the ads shown to them. But frequently, the ad content is provided by an outside source. Publishers are often hesitant to share all the information they have about their users for various reasons. At the same time, they would still prefer to give their users the benefits of having the ads that are directed in a meaningful way.